This invention relates to rolling mills for rolling sheet, plate, and the like. More particularly, the invention relates to rolling mills for rolling relatively thick workpieces of composites or special steel alloys such as, for example, alloys used for armor plate.
In the rolling of special steel alloys, a very high pressure must be exerted upon the workpiece by the reducing rolls of a rolling mill. This pressure, generally measured in terms of the separation force of the reducing rolls, may be required to be in the millions of pounds, depending upon the particular alloy, the thickness and width of the workpiece, the configuration of the reducing rolls, and the number of passages used to effect a given reduction in thickness of the workpiece. As more sophisticated alloys have been developed with increased strength and toughness, there has been a growing need for rolling mills of greater pressure capacity.
One of the difficulties in scaling up present rolling mills to increase pressure capacity is related to the configuration of the reducing rolls. To allow for the deflection of the reducing rolls under pressure, the reducing rolls of conventional rolling mills are formed with a crown; the reducing rolls have a smaller diameter at their ends than at their intermediate points. Such reducing rolls are designed to deflect to a uniform spacing only at a single separation force; any other separation force will result in too much or too little deflection of the reducing rolls, causing the workpiece to have a nonuniform thickness.
Another difficulty in producing a rolling mill of increased pressure capacity suitable for special alloys is related to the drive means. Generally, the reducing rolls of conventional rolling mills are driven by stationary motors connected to the reducing rolls by drive shafts having universal joints. The reducing rolls may be geared together or otherwise synchronized to ensure similar rotating speeds. Examples of such drive means are the rolling mills disclosed in U.S. Pat. No. 2,752,803 (Antrim), U.S. Pat. No. 3,605,474 (Lhenry), and U.S. Pat. No. 4,152,912 (Shiozaki et al).
The universal joints of the drive means of these conventional rolling mills cause oscillations in the rotataional speed of the reducing rolls, and the backlash of the gears and the twisting of the reducing rolls aggravate these oscillations in the rotational speed. Even if small, such variations may prove significant in the rolling of special alloys, particularly when a rolling mill is scaled up to handle relatively large workpieces. Other difficulties result from slight variations between the rotational speeds of the upper and lower reducing rolls.
To maintain maximum strength and toughness, great care must be directed to maintaining the metallurgical integrity of special alloys. If the upper and lower reducing rollsare not both rotated at precisely the same speed along their full operating length, such variations, even if small, will cause slippage or disturb the crystal structure at the surface, reducing the suitability of the workpiece for particular uses, such as, for example, armor plate. A technique known as "warm rolling", in which the temperature of the workpiece is relatively low but above the temperature of cold rolling, is of some help in maintaining the metallurgical integrity of special alloys.
Similarly, there is a need for a rolling mill of larger pressure capacity for hot or cold rolling of super alloys that are particularly difficult to work. Larger capacity rolling mills are also required to achieve deeper penetration of the metallurgical structure of a workpiece during the rolling and for decreasing the number of passes required to effect a given reduction in thickness or other change of shape of a workpiece during form rolling. Also, larger capacity rolling mills are required for the rolling of composite and metal laminates.
Accordingly, it is an object of the present invention to provide a rolling mill having increased capacity, as measured in terms of the separation force, suitable for rolling relatively large workpieces made of special alloys, composites and metal laminates.
it is a further object of the present invention to provide a rolling mill capable of reducing a workpiece to a uniform thickness over a wide range of separation forces rather than at a single separation force.
It is still a further object of the present invention to provide a rolling mill with improved uniformity of rotational speeds of the upper and lower reducing rolls along their full operating lengths so as to prevent slippage and maintain the metallurgical integrity of a workpiece.